1. Field of the Invention
The present invention relates to a swing type input apparatus in which an angle of rotation of a swingable operation knob can be detected by detecting means, and particularly, relates to a swing type input apparatus using a magnetic sensor as detecting means.
2. Description of the Related Art
Regarding a related-art input apparatus in which an angle of rotation of a swingable operation knob is detected by a magnetic sensor to obtain a predetermined input signal, Japanese Unexamined Patent Application Publication No. 2001-118465 discloses a switch apparatus capable of generating a signal for driving an automatic-window opening and closing motor. In the related-art input apparatus (switch apparatus), a circuit mechanism including, for example, a magnetic sensor, a relay, and a signal processing circuit is covered with, for instance, a resin case to prevent the entry of water or dust. An operation knob is placed above the resin case such that the knob is swingably supported. A magnet swinging with the operation knob is placed near the resin case. When the magnet swings, the magnet moves close to or away from the magnetic sensor. Thus, a magnetic field, produced by the magnet, detected by the magnetic sensor varies so that a signal depending on a rotation position of the operation knob is extracted. For example, when the magnetic sensor detects rotation of the operation knob to a predetermined pushed position, a signal to allow the motor to rotate forward is output, thus opening the automatic window. When the magnetic sensor detects backward rotation of the operation knob to a predetermined pulled position, a signal to allow the motor to rotate backward is output, thus closing the automatic window.
In the above related-art swing type input apparatus, the magnet has to be placed near the magnetic sensor incorporated below the operation knob. Accordingly, the magnet is also attached below the operation knob. When the magnet is swung in a position at a certain distance from the center line of rotation (hereinafter, referred to as “rotation center line”) of the operation knob, however, the difference between the rotation of the operation knob and that of the magnet can easily occur. Disadvantageously, higher detection accuracy may not be expected in the related-art input apparatus. It is difficult to extract an analog input signal by, for example, finely detecting an angle of rotation of the operation knob.
The magnet and the magnetic sensor may be arranged near the rotation center line of the operation knob. In this case, the magnetic sensor is positioned near a user's finger. It is therefore necessary to provide electrostatic shielding so that the user is not affected by charged static electricity. In addition, an object (e.g., a magnetic wristband) functioning as a magnetic field source may be placed on or near the operation knob. Accordingly, it is necessary to magnetically shield the magnet and the magnetic sensor. If special measures are not taken in consideration of the above-described problems, the magnet and the magnetic sensor are easily affected by static electricity or an external magnetic field even when the magnet and the magnetic sensor are arranged in an area effective in increasing the detection accuracy. Disadvantageously, it may be difficult to ensure high reliability.